I. Field of Invention
The present invention is directed to a heating, ventilation, and air-conditioning system and more particularly relates to a method and system for optimizing the torque of a compressor motor by varying at least one of a voltage or a capacitance.
II. Description of the Related Art
Conventional single-phase alternating current induction motors for driving compressors are connected to a source of power by a line contactor. Electric motors typically include a stator, which is wound with a start winding and run winding connected to the source of power. The stator winding surrounds the motor, which rotates a shaft to produce the motor output. In circuit with the run winding and the start winding are, if required, a run capacitor and a start capacitor, respectively. Start capacitors is usually sized for a capacitance that is appropriate for starting the compressor while a run capacitor is usually sized for a capacitance that is appropriate for the maximum running torque of the compressor.
In capacitor start motors, start circuits are connected in parallel with a run winding of each speed of the multi-speed motor. The start circuits include a start winding which is connected in series with start capacitors. During a motor start, both the run winding and the start winding are connected across the motor""s power source to magnetically excite the rotor and cause rotation. The start winding and start capacitor combination is used to provide the high torque required during typical start conditions.
With past approaches, conventional motors for driving compressors provide more than enough torque to satisfy the demands of the compressor. With variable capacity compressors, the motor driving the compressor may significantly vary torque. For example, in a two-stage, reversible compressor, the motor may provide a large amount of torque in a second stage of operation and a lesser amount of torque in the first stage of operation. However, although past approaches significantly varied the capacity of the compressor, past approaches failed to optimize the torque of the compressor motor for a given load, resulting in inefficient operation of the compressor.
Accordingly, the present invention is directed to motor optimization by varying at least one of a voltage and a capacitance based on changing demands for heating or cooling. Moreover, the present invention is directed to motor optimization of a two-stage compressor that operates in a second stage when the motor rotates in one direction and operates in a first stage when the motor rotates in the reverse direction.
An object of advantage of the present invention is to provide an improved system and method of operating a compressor motor that minimizes one or more of the limitations and disadvantages of the presently available systems and methods for such compressor motors and heating, ventilation, and air conditioning (hereinbelow HVAC) systems.
Additional features and advantages of the invention will be set forth in part in the description which follows and in part will be obvious from the description, or may be learned by practice of the invention. The objectives and advantages of the invention may be realized and attained by the systems and methods particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, there is provided a method for controlling a two-stage, reversible compressor, such as the Bristol Twin Single compressor. Compressors of this type and their use and application are explained in detail in U.S. patent application Ser. No. 09/133,841, filed on Aug. 13, 1998, now U.S. Pat. No. 6,132,177 and entitled xe2x80x9cTwo Stage Reciprocating Compressors and Associated HVAC Systems and Methods,xe2x80x9d and in U.S. patent application Ser. No. 09/235,288, having a filing date of Jan. 22, 1999, now U.S. Pat. No. 6,217,287 and entitled Variable Capacity Compressor Having Adjustable Crankpin Throw Structure, both of which applications are hereby incorporated by reference. Such compressors operate at a first stage when the motor rotates in one direction and at a second stage when the motor rotates in a reverse direction. By means of example, such a compressor with two cylinders may reciprocate the pistons in both cylinders at one stage and will reciprocate only one piston at the other stage. Such a compressor having only a single cylinder will reciprocate the piston at full stroke when the motor rotates in one direction and at a lesser stroke (e.g., a half stroke) when the motor rotates in the other direction.
The method of controlling a variable capacity compressor driven by a motor. The method including, for example, operating the variable capacity compressor at a first capacity to satisfy a demand for heating or cooling; detecting a change in the demand for heating or cooling; operating the variable capacity compressor at a second, different capacity based on the detected change in demand; detecting an operating parameter that can indicate an opportunity to increase compressor efficiency when the compressor is operating at a given capacity; and varying the torque applied by the motor when the detected operating parameter indicates an opportunity to increase efficiency of the compressor by varying the torque.
Moreover, in another embodiment, there is provided a system for controlling a variable capacity compressor including a start winding and a run winding, including, means for operating the variable capacity compressor in one or more stages such that the power is provided by the variable capacity compressor to satisfy a demand for heating or cooling; means for detecting a change in the demand for heating or cooling; means for operating the variable capacity compressor at a reduced capacity based on the detected change; and means for varying one of a voltage applied to the variable capacity compressor or a capacitance connected in parallel with a run capacitor, such that the torque provided to the variable capacity compressor varies to increase the efficiency of the compressor.
In still another embodiment, there is provided a system for controlling a variable capacity compressor including a start winding and a run winding, including, for example, a sensor for detecting an indication of a change in the demand for heating or cooling; a controller further including means for operating the variable capacity compressor in one or more stages such that the power is provided by the variable capacity compressor to satisfy a demand for heating or cooling, and means for operating the variable capacity compressor at a reduced capacity based on the detected change. Moreover, the system includes a first relay and a second relay connected to the controller, such that the first and second relays may vary a capacitance connected in parallel with a run capacitor, wherein the torque provided to the variable capacity compressor varies to increase the efficiency of the compressor.
In yet another embodiment, there is provided a computer readable medium containing computer software, which, when run on a computer causes the computer to provide apparatus for controlling a variable capacity compressor including a start winding and a run winding. The apparatus includes, for example, means for operating the variable capacity compressor in one or more stages such that the power is provided by the variable capacity compressor to satisfy a demand for heating or cooling; means for detecting a change in the demand for heating or cooling; means for operating the variable capacity compressor at a reduced capacity based on the detected change; and means for varying one of a voltage applied to the variable capacity compressor or a capacitance connected in parallel with a run capacitor, such that the torque provided to the variable capacity compressor varies to increase the efficiency of the compressor.
Moreover, in an embodiment, there is provided a system for controlling a variable capacity compressor including a start winding and a run winding, the system including at least one memory including, for example, code that operates to control the variable capacity compressor in one or more stages such that the power is provided by the variable capacity compressor to satisfy a demand for heating or cooling, code that detects a change in the demand for heating or cooling, code that operates the variable capacity compressor at a reduced capacity based on the detected change, and code that varies one of a voltage applied to the variable capacity compressor or a capacitance connected in parallel with a run capacitor, such that the torque provided to the variable capacity compressor varies to increase the efficiency of the compressor. Moreover, the system includes at least one processor that executes the code.
Furthermore, in still another embodiment, there is provided a system of controlling a two-stage reversible compressor including a start winding and a run winding, including, for example, means for operating the variable capacity compressor in one or more stages such that the power is provided by the variable capacity compressor to satisfy a demand for heating or cooling; means for detecting a change in the demand for heating or cooling; means for operating the variable capacity compressor at a reduced capacity based on the detected change; and means for varying a capacitance connected in parallel with a run capacitor, such that the torque provided to the variable capacity compressor varies to increase the efficiency of the compressor.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as described.